The present invention relates in general to electrical systems for motor vehicles equipped with solar panels for generating electricity, and, more specifically, to variable voltage converters for such systems.
Power generation using solar panels (e.g., photovoltaic arrays) has received increasing attention in the automotive industry due to their dropping price and improved efficiency levels now available. Solar panels can be attached to a vehicle roof or can be used to replace a moon-roof or sun-roof, for example. Electricity generated by the panels can be used to charge an onboard battery (such as an auxiliary battery, an electric vehicle's high voltage battery, or the main 12V battery of a gasoline-powered vehicle). A charge controller (e.g., a Maximum Power Point Tracking, or MPPT, controller) is used to ensure that a maximum amount of power is transferred from the solar panel to the load (e.g., battery being charged). More specifically, it is known that to deliver maximum power to a load, the power source (including solar panels) should have the same internal impedance as the impedance of the load. An MPPT module typically includes a DC-to-DC voltage converter (VC) placed between the photovoltaic (PV) array and the battery load. By converting the PV output voltage to the battery voltage, the VC presents an ideal load to the PV array allowing it to operate at its optimum voltage and maximum power transfer. Generally, the DC-DC regulator (converter) in MPPT charge controllers can be a boost, buck, buck-boost, SEPIC or any other type of converter. The proper topology can be selected based on the output voltage of solar panel and input voltage of the load. Two of the most popular types of converters which have been employed for MPPT are boost converter and buck converters.
Depending upon the relative magnitudes of the PV and battery voltages, up to one-half of the generated power would be lost if a voltage converter was not used. However, the MPPT module results in a significant increase in the overall cost of a solar charging system.